The Lawrence Livermore National Laboratory tries to answer those questions each year in the form of a "flow" diagram. On the left side of the diagram are the different forms of energy that are produced in or imported to the U.S. and on the right are the eventual uses to which this energy is put. On the top left the yellow bar represents the solar energy produced in 2013. At the bottom left the wide green bar represents petroleum products that were used as energy. The left side bars go from the least carbon intensive energy forms (solar, nuclear, hydro) down to the most carbon intense forms of energy (coal, biomass, petroleum).

This is a Sankey diagram in which the size of the pipes or "spaghetti noodles" indicate the relative amounts of energy flowing. Petroleum was by far the largest energy source in 2013 as well as the most polluting.

On the right side of the diagram are four pink boxes which are the four final uses to which energy is put in the U.S. economy. One way to think about it is that most energy is used in buildings (the three top pink boxes) - factories, homes, places of business - and the second way energy is used is for transportation (the bottom pink box). Trucks, cars, marine vessels, trains, airplanes use a great deal of energy and most of it is in the form of liquid fuels such as diesel, gasoline, aviation fuel, kerosene and other petroleum products.

There is also a light grey image in the background called "rejected energy". This is the energy that is generated and distributed but never gets put to good use. It is energy that is lost on transmission lines, that is wasted in inefficient cars and homes that are poorly built. It is energy that was used to produce, transport and cook food that was thrown away.

Not all energy can be used under current technologies but energy efficient homes, factories and cars can go a long way to reducing waste. All of the costs, including environmental damage that goes into producing energy, is avoided with efficient processes.

This diagram is a snapshot of the U.S. energy flow in 2013. The flows have been changing over time. For example coal use has probably peaked and is now likely to get smaller each year. Solar and wind are growing. This diagram would look very different if it were made for other countries. France gets most of its electricity from nuclear power plants, for example, and Denmark has a great deal of wind power.

China uses a great deal of coal to fuel its economy which causes both health hazards and political protest. The article linked below shows how China is shifting its energy forms - and also how inefficient its energy system is in meeting the needs of its society.